Rollup merge of #101381 - Urgau:target-mixup-homogenous-floats, r=Amanieu

Test that target feature mix up with homogeneous floats is sound

This pull-request adds a test in `src/test/abi/` that test that target feature mix up with homogeneous floats is sound.

This is basically is ripoff of [src/test/ui/simd/target-feature-mixup.rs](https://github.com/rust-lang/rust/blob/47d1cdb0bcac8e417071ce1929d261efe2399ae2/src/test/ui/simd/target-feature-mixup.rs) but for floats and without `#[repr(simd)]`.

*Extracted from https://github.com/rust-lang/rust/pull/97559 since I don't yet know what to do with that PR.*